A Photonic-Based Self-Interference Cancellation Approach for Continuous-Wave Radar Systems

A photonic-based self-interference cancellation (SIC) method for the continuous-wave radar is proposed based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) in the DP-QPSK modulator is biased as a carrier-suppressed single-sideband (CS-SSB) modulator to modulate the received signal, which includes both the useful echo signal reflected by the target and the self-interference signal from the transmitting antenna. The lower DP-MZM in the DP-QPSK modulator is also biased as a CS-SSB modulator, where the reference signal is modulated after amplitude and delay adjustments. After the two optical signals are coupled in a polarizer, the reference signal and the self-interference signal cancel each other in the optical domain. By properly controlling the carrier suppression of the upper modulator, the coupled optical signal consists of one first-order optical sideband and an optical carrier, so the useful echo signal without self-interference can be recovered by photodetection. Simulation results show that the proposed SIC system can effectively suppress the self-interference signal. System parameters that affect the SIC are further verified and studied by simulation.